Ah, that's because Joomla 4.2 has replaced $this->app with $this->getApplication() in plugins. Yeah, I had reported to the project that this kind of change without a fallback in a magic __get would cause exactly this kind of problem because it's really hard finding all instances of this code across all plugins in a developer's portfolio without false positives or false negatives. Well, it looks like I was right. Sigh…
Please install this dev release https://www.akeeba.com/download/admin-tools-professional/7-2-1-dev202212150737-rev6d5bf651.html and let me know if it fixes this issue for you as I see it does for me. If I can get confirmation I'll make a bug fix release tomorrow. I consider broken automation to be a high priority issue which warrants an emergency release.
Thank you in advance and thank you again for your issue report!
Nicholas K. Dionysopoulos
Lead Developer and Director
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